This invention relates to skin electrodes, and more particularly to pregelled disposable medical electrodes used to detect biological or physiological electrical potentials such as those associated with muscular activity. In more detail, this invention relates to low cost, high quality pregelled electrocardiogram (ECG) electrodes for detecting the muscular activity of the human heart.
Most ECG electrodes in routine use today depend on a metal-electrolyte interface with the body surface. Many electrodes use extremely pure silver as the metallic component. Those in which a moist, ready-to-use electrolytic paste is packaged as part of the electrode are termed pre-gelled. Electrodes intended for single patient use only are considered disposable. Those that can be reused many times are termed permanent.
In the past, the only high quality electrodes available contained pure silver as the metallic component of the electrode, with the surface often chlorided to achieve optimum performance. The process of chloriding involves coating, either by electrodeposition or reaction with chlorine gas, of the active surface of the silver with a thin layer of silver chloride.
Conventional permanent ECG electrodes are available in many styles and configurations, but all share several negative characteristics, these characteristics not being evident in the present invention:
(a) They are often relatively expensive, since most employ high cost construction materials and methods. PA1 (b) They must be reprocessed (cleaned carefully) between uses. PA1 (c) They must be attached to the skin with separate straps, suction cups, glue, tape, adhesive pads, or similar means. PA1 (d) Most require that electrolytic gel or fluid be applied to the skin (or electrode) at time of use. PA1 (e) Most are "short term" electrodes (in the sense that they cannot be left on a patient for more than a few hours before the gel desiccates and loses its electrical contact with the skin).
On the positive side, the best properly-prepared permanent ECG electrodes are capable of delivering extremely high resolution, nearly artifact-free signals. Hence, they are used whenever very high quality "Type I" ECG recordings are necessary. Further, if preparation and reprocessing costs are ignored. the cost/use is low, compared to pregelled, single-use electrodes. Suction or strap-attached permanent electrodes are often used when short-term ECG's are needed, since the electrodes can be repositioned or moved as often as necessary without resorting to the use of tape or glue.
Conventional disposable ECG electrodes offer increased convenience over permanent electrodes. Disposable ECG electrodes are usually pregelled, self-adhesive, and clean. Since they cannot be reused, crosscontamination is minimized and postuse cleanup is minimal. Most electrodes of this type provide reasonably accurate transduction of ECG data and are a fairly cost-effective approach to routine diagnostic ECG's and heart rate monitoring. Most will function adequately for one to several days, depending on the patient.
Pregelled electrodes typically consist of a thin, adhesive coated disc of open or closed cell foam or microporous tape. A centrally located gel reservoir consisting of a molded cup, such as shown in U.S. Pat. Nos. 3,696,807, 3,701,346, 3,713,435, 3,820,531 or 3,830,229, or a die cut hole in the foam, such as shown in U.S. Pat. No. 3,868,946, encapsulates a gel-saturated open cell compressible foam column. In the alternative, the gel-saturated, open cell foam column may be adhered directly to the face of the disc of foam, such as in U.S. Pat. No. 3,828,766, or to an impermeable backing material as in U.S. Pat. No. 3,805,769. The consistency of the gel is maintained by sealing the opening of the gel reservoir in one of several ways, which include: an injection molded or thermo-formed cap removably attached to the gel cup or an adhesive coated film on the disc in conjunction with a moisture-proof backing paper attached to the film and covering the gel saturated foam column or a combination of these. In spite of the use in these electrodes of such means for sealing the gel reservoir, most also require a secondary air-tight foil pouch or plastic bag to contain the electrode in an air-tight way and preserve the gel in a usable condition.
All pregelled electrodes known to be presently available, incorporate a metallic component in contact with the gel. This component can be silver coated plastic, silver, nickel, or stainless steel. In some types of electrodes, lead wires are permanently attached to the electrode. In the majority, however, a male snap fastener of silver, stainless steel, nickel, etc., is incorporated as a part of the electrode. A lead wire having a mating metallic female snap fastener on one end is connected to the male snap fastener of the electrode. The opposite end of such lead wire is then secured to a diagnostic instrument, such as a cardiograph. As an alternative, a silver-coated plastic snap fastener, such as shown in U.S. Pat. No. 3,841,312 may be used. Use of mating snap fasteners have the disadvantage that relative movement between the electrode and the lead may cause motion artifacts. Further, use of a coated plastic male snap in conjunction with a metallic female snap may result in the silver coating on the male snap being scratched off during application or usage, causing faulty readings.
U.S. Pat. No. 3,599,629 shows an electrode which does not employ a snap fastener. Instead, this device has a flat, wafer-like top composed of an electrically insulating material coated with a thin film of metallic silver having a surface layer that has been converted to silver chloride. Rather than using a wire lead having a mating snap fastener, this electrode employs a tubular plug dimensioned to snugly fit into a corresponding silver chloride coated socket in the wafer-like top, electrical continuity resulting from intimate contact between the socket and the plug.
In all of the above instances, the pregelled electrodes are sold ready for use having an electrically conductive material, such as metal or a metal chloride, in contact with the electrolyte gel. Such contact presents the possibility of chemical reaction between the two during storage of the electrode prior to usage. In addition, in all known conventional pregelled electrodes, especially those containing silver or silver chloride, the metal component represents a considerable portion of the cost of the electrode. As the electrodes are disposed of after only one use, the cost of the metal adds considerably to the cost of usage of same.